Here are the correct forms of the words:

1. My brother **occasionally** flies to Hong Kong on business. (occasion)
2. The most popular after-school **activities** here are football and badminton. (act)
3. These shoes look nice but they are terribly **uncomfortable**. (comfort)
4. The year-end party was not so **enjoyable** and we left early. (enjoy)
5. **Unfortunately**, he failed the driving test for the second time. (luck)
6. There were fifty **competitors** in the talent contest last year. (compete)
7. The **destruction** of most of London was brought about in 1666. (destroy)
8. Every week there are two **flights** from Bangkok to Hanoi. (fly)